Private onsen in Tokyo
A bath you have to yourself: no other bathers, and usually no tattoo problem either.
Is there a mixed onsen in Tokyo?
Not one we have found. Mixed bathing (konyoku) survives at mountain, riverside and seaside baths, and we have not recorded one in Tokyo. If what you want is to bathe together as a couple or a family, a private onsen is usually how it is done in Japan: the 2 below have a bath your group uses alone. Where Japan’s mixed baths are, and what to wear
Day trips from Tokyo
The same list for places you can reach from Tokyo and be back the same day.